No autothrottles after installing the PMDG 737NG 800/900 or autothrottle switch will not latch

This is caused failure to follow the Normal Checklist. Engine generators
on the overhead panel are not selected ON after engine start, which
causes the autothrottle switch to disarm. Turn ON the generator by
cycling the GEN switch to ON momentarily and ensuring the Blue Gen off
Bus light is out and the problem should be corrected.